1. Field of the Invention
This invention relates to a sheet feeder for feeding a sheet to a printing unit such as a printer, a copying machine or a recording unit in an image copying machine. More particularly, it is drawn to a sheet feeder capable of executing both an automatic sheet feeding operation and a manual sheet feeding operation.
2. Description of the Related Art
Among sheet feeders provided with both an automatic sheet feeding function and a manual sheet feeding function, one type, as illustrated in FIG. 9, is well known. In the known type of sheet feeder, a sheet cassette 104 holding a plurality of stacked sheets 102 is incorporated in the sheet feeding mechanism of a device such as a printer or a copying machine. In the sheet feeding mechanism, there is disposed a first sheet feeding roller 106 for the automatic sheet feeding operation. The sheets 102 stacked in the sheet cassette 104 are fed in order from the top to a recording unit 108 using a frictional force generated by the rotation of the first sheet feeding roller 106.
In addition, a second sheet feeding roller 110 and a pressure roller 112 for a manual sheet feeding operation are arranged in a manual sheet feeding passage 114. The sheet is fed to the recording unit 108 while being held between the rollers.
In this type of sheet feeder, however, special mechanisms are required for the automatic sheet feeding operation and the manual sheet feeding operation, respectively, with attendant problems caused by the large number of component parts and complicated mechanisms leading to difficulties in assembly and a high failure rate.